Scroll compressor and method for controlling back pressure for the same

ABSTRACT

A scroll compressor has a fixed scroll member, a movable scroll member, a housing. The housing is secured to the fixed scroll member. The housing accommodates the movable scroll member to define a back pressure chamber. Pressure in the back pressure chamber is applied to the back surface of a movable scroll base plate of the movable scroll member. The back pressure chamber communicates with a region through a communication passage. The region is lower in pressure than the back pressure chamber. The communication passage relieves the pressure in the back pressure chamber to the region. The communication passage includes a valve. The valve varies an opening amount of the communication passage due to difference between the pressure in the compression region in the predetermined period of a compression process of the gas, and the pressure in the back pressure chamber.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a scroll compressor and more particularly to a device and a method for controlling pressure in a back pressure chamber on the back surface of a movable scroll member of the scroll compressor.

[0002] Generally, a scroll compressor includes a fixed scroll member and a movable scroll member each having a base and a spiral wrap extending from the base. One spiral wrap is engaged with the other to form a compression region between the fixed scroll member and the movable scroll member. As the movable scroll member orbits relative to the fixed scroll member, refrigerant gas in the compression region decreases its volume. Such a scroll compressor has sealing surfaces on respective end surfaces in axial directions of the spiral wraps. When back pressure is applied to the back surface of the movable scroll member, thrust force acts on the fixed scroll member, thereby sealing the refrigerant gas between the fixed scroll member and the movable scroll member.

[0003] While the compressor is driven, refrigerant gas in high pressure is intermittently discharged. Therefore, the back pressure varies. That is, the thrust force varies. If the created thrust force becomes too large, it causes sliding surfaces between the fixed scroll member and the movable scroll member to be worn while sealing performance is improved. For the above reason, it is required that a device and a method for controlling pressure in the back pressure chamber when the pressure becomes extremely high.

[0004] Unexamined Japanese Patent Publication No. 57-76291 discloses such a scroll compressor. The scroll compressor has an opening and closing valve arranged in a communication passage to communicate a back pressure chamber with an intake passage. A spring urges the opening and closing valve to close the communication passage. When the pressure in the back pressure chamber becomes extremely high, the opening and closing valve opens the communication passage due to the high pressure in spite of resilient force of the spring. At this time, refrigerant gas in the back pressure chamber flows into the intake passage through the communication passage. The flow of the refrigerant gas prevents the above scroll compressor from being damaged by the extreme high pressure in the back pressure chamber. That is, the above scroll compressor has a pressure relief valve functioning as a safety valve.

[0005] In the above prior art, however, when force applied to the opening and closing valve by the pressure in the back pressure chamber exceeds the resilient force of the spring, the refrigerant gas in the back pressure chamber flows into an intake system. Thus, the spring is required.

SUMMARY OF THE INVENTION

[0006] The present invention addresses a control of pressure in a back pressure chamber for a scroll compressor.

[0007] To achieve the above object, the present invention has following features. A scroll compressor compresses gas introduced from an inlet. The gas is compressed and discharged through a discharge port. The scroll compressor has a fixed scroll member, a movable scroll member and a housing. The movable scroll member has a movable scroll base plate. The fixed scroll member and the movable scroll member cooperatively form a compression region and an intake space communicating to the inlet. The housing is secured to the fixed scroll member. The housing accommodates the movable scroll member to define a back pressure chamber. Pressure in the back pressure chamber is applied to the back surface of the movable scroll base plate. The back pressure chamber communicates with a region through a communication passage. The region is lower in pressure than the back pressure chamber. The communication passage includes a valve. The communication passage relieves the pressure in the back pressure chamber to the region. The valve varies an opening amount of the communication passage due to difference between the pressure in the compression region in the predetermined period of a compression process of the gas, and the pressure in the back pressure chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0009]FIG. 1 is a diagram in a longitudinal cross-sectional view illustrating a scroll compressor according to the present invention;

[0010]FIG. 2 is a transverse cross-sectional view of FIG. 1, which shows communication between a compression region and a second chamber; and

[0011]FIG. 3 is a partial enlarged view of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A scroll compressor and a method for controlling back pressure for the scroll compressor, according to a preferred embodiment of the present invention will be described with reference to FIGS. 1 through 3.

[0013] As shown in FIG. 1, a fixed scroll member 2, a center housing 4 and a motor housing 6 constitute a casing for sealing a scroll compressor 1. In the scroll compressor 1, a movable scroll member 20 and its drive mechanism are accommodated. The center housing 4 is secured to the fixed scroll member 2 at its front end, and is secured to the motor housing 6 at its rear end. A drive shaft 8 is rotatably supported in the center housing 4 and the motor housing 6 respectively by radial bearings 10 and 12. A crankshaft 14 is eccentrically arranged with respect to the drive shaft 8 and is integrally formed at the front end of the drive shaft 8.

[0014] Still referring to FIG. 1, the fixed scroll member 2 has a fixed scroll spiral wrap 28 extending from the surface of a disk-shaped fixed scroll base plate 26. In the same manner, the movable scroll member 20 has a movable scroll spiral wrap 30 extending from the front surface of a disk-shaped movable scroll base plate 24. The spiral wraps 28 and 30 are engaged with each other. A fixed scroll tip seal 28 aoccupies a groove in the end surface of the fixed scroll spiral wrap 28, and a movable scroll tip seal 30 a occupies a groove in the end surface of the movable scroll spiral wrap 30.

[0015] The fixed scroll base plate 26 and fixed scroll spiral wrap 28 of the fixed scroll member 2 and the movable scroll base plate 24 and movable scroll spiral wrap 30 of the movable scroll member 20 cooperatively form compression chambers 32 defined between the scroll members 2 and 20 as a compression region, since the spiral wraps 28 and 30 contact at plural points. The compression chambers 32 are sealed spaces. The movable scroll member 20 orbits in accordance with the rotation of the crankshaft 14. At this time, a balance weight 18 cancels centrifugal force generated by orbital motion of the movable scroll member 20. The crankshaft 14 which integrally rotates with the drive shaft 8, a bushing 16, and a needle bearing 22 interposed between the crankshaft 14 and a boss 24 a of the movable scroll member 20 constitute an orbiting mechanism for transmitting the rotation of the crankshaft 14 to the movable scroll member 20.

[0016] A pair of planes 14 a and 14 a, which are mutually parallel planes, are formed on the circumferential surface of the crankshaft 14. The crankshaft 14 is fitted in the bushing 16 so as to integrally rotate with the bushing 16 through the planes 14 a and 14 a. The balance weight 18 is coupled to one end of the bushing 16 so as to integrally rotate with the bushing 16. The movable scroll member 20 is coupled to the other end of the bushing 16 through the needle bearing 22 so as to relatively rotate with the bushing 16 while facing to the fixed scroll member 2. Also, the needle bearing 22 is accommodated in a cylindrical boss 24 a of the movable scroll member 20. The boss 24 a is formed on the back surface, which is the right side with respect to the movable scroll member 20 in FIG. 1, of the movable scroll base plate 24 so as to protrude therefrom .

[0017] An annular first seal 76 occupies an annular recess in the outer circumferential surface of the bushing 16 facing to the inner circumferential surface of the boss 24 a. The first seal 76 functions to prevent the refrigerant gas from leaking from a first pressure chamber 70 as a high pressure region into the rest of a backside region adjacent to the back surface of the movable scroll base plate 24 through a clearance between the movable scroll member 20 and the center housing 4 as much as possible.

[0018] Also, an annular second seal 78 occupies an annular recess in the front end of the center housing 4 facing to the movable scroll base plate 24. The second seal 78 functions to separate the rest of the backside region into a second pressure chamber 72 as an intermediate pressure region and a third pressure chamber 74 as a low pressure region. The third pressure chamber 74 communicates with the compression chambers 32 adjacent to an inlet 44. Accordingly, the refrigerant gas in the first pressure chamber 70 tends to leak into the rest of the backside region adjacent to the back surface of the movable scroll base plate 24 by way of the second pressure chamber 72 and the third pressure chamber 74 in order.

[0019] Besides, the first seal 76 is disposed between the first pressure chamber 70 and the second pressure chamber 72 so as to define the first pressure chamber 70 and the second pressure chamber 72, and the second seal 78 is disposed between the second pressure chamber 72 and the third pressure chamber 74 so as to define the second pressure chamber 72 and the third pressure chamber 74. Thereby, sealing efficiency is reinforced. Accordingly, the amount of the refrigerant gas leaking into the rest of the backside region adjacent to the back surface of the movable scroll base plate 24 is reduced.

[0020] The back pressure region is constituted of the first pressure chamber 70, the second pressure chamber 72 and the third pressure chamber 74. The pressure in the back pressure region is applied to the back surface of the movable scroll base plate 24.

[0021] A reed-type discharge valve 52, which opens and closes a discharge port 50, is affixed to the movable scroll base plate 24 at its back surface facing to the crankshaft 14. This discharge valve 52 has a reed valve 54 at the discharge port 50, a retainer 56 for regulating the reed valve 54 and a bolt 58 for connecting respective ends of the reed valve 54 and the retainer 56 to the movable scroll base plate 24. The discharge valve 52 is accommodated in a discharge valve chamber 25 which is bored at the back surface of the movable scroll base plate 24.

[0022] The reed valve 54 opens and closes the discharge port 50 due to pressure difference between the compression chamber 32 communicating with the discharge port 50 and the first pressure chamber 70. That is, when pressure in the compression chamber 32 is higher than that in the first pressure chamber 70, the reed valve 54 opens the discharge port 50. When the pressure in the compression chamber 32 is lower than that in the first pressure chamber 70, the reed valve 54 closes the discharge port 50. Also, the retainer 56 is not only designed to retain the reed valve 54 but also designed to regulate the maximum opening amount of the reed valve 54.

[0023] As shown in FIGS. 1 and 2, the movable scroll member 20 orbits about a center 2 aof the fixed scroll member 2. In the movable scroll base plate 24 of the movable scroll member 20, a communication passage 60 for relieving pressure is formed to communicate the second pressure chamber 72 with an intake space 45. Also, a spool valve 62 as an opening and closing valve is formed to open and close the communication passage 60. The intake space 45 corresponds to an intake system according to the present invention. The intake system is defined as a region in the compressor including refrigerant gas in low pressure, which is returned from an external refrigerant gas circuit and has not been introduced into the compression chamber 32. Therefore, if the communication passage 60 communicates with the above region, it is not required that the communication passage 60 communicates with the intake space 45.

[0024] As shown in FIG. 3, pressure in the second pressure chamber 72 is applied to a first end surface 62 ain the direction of the spool valve 62 through a first pressure port 66 for communicating with the second pressure chamber 72. Pressure in the compression chamber 32 is applied to a second end surface 62 b in the direction of the spool valve 62 through a second pressure port 64 for communicating with the compression chamber 32. The spool valve 62 opens and closes the communication passage 60 due to difference between the pressure applied to the first end surface 62 aand the pressure applied to the second end surface 62 b.

[0025] Still referring to FIG. 3, the second pressure port 64 is formed at an optionally fixed place in the compression chamber 32 in a predetermined compression period so that pressure in an intermediate pressure region is applied to the spool valve 62. The second pressure port 64 communicates with the compression chamber 32, while refrigerant gas in a predetermined sealed compression part in the compression chambers 32 is compressed during the predetermined compression period where the movable scroll member 20 orbits by an angle of 360 degrees. That is, the second pressure port 64 is formed to communicate with the compression chamber 32 as the intermediate pressure region.

[0026] In the embodiment, the spool valve 62 has a step. The area of the second end surface 62 b to which the pressure in the compression chamber 32 is applied is smaller than that of the first end surface 62 ato which the pressure in the second pressure chamber 72 is applied. A cylindrical stopper 68 regulates maximum movement of the spool valve 62 to close the communication passage 60.

[0027] As shown in FIG. 1, a plurality of recesses 41 for preventing self rotation such as four recesses is formed in an equiangular position on an identical circumference of the front end surface of the center housing 4. Movable pins 40 fixed to the movable scroll base plate 24 are loosely fitted into the associated recesses 41 so as to contact fixed pins 42 fixed to the center housing 4. The recesses 41, the movable pins 40 and the fixed pins 42 prevent the movable scroll member 20 from rotating about an axis of the movable scroll member 20, while the crankshaft 14 rotates. That is, the recesses 41, the fixed pins 42 and the movable pins 40 constitute mechanism for preventing self rotation of the movable scroll member 20.

[0028] Still referring to FIG. 1, a stator 46 is fixed on the inner circumferential surface of the motor housing 6, and a rotor 48 is fixed on the drive shaft 8. The stator 46 and the rotor 48 constitute a motor.

[0029] The rotor 48 and the drive shaft 8 integrally rotate by energizing the stator 46.

[0030] In the above scroll compressor, as the crankshaft 14 of the drive shaft 8 rotates, the movable scroll member 20 orbits. The refrigerant gas introduced into the intake space 45 through the inlet 44 which is formed through the fixed scroll member 2 flows from the peripheral side of both the scroll members 2 and 20 into the space between the fixed scroll base plate 26 and the movable scroll base plate 24. Also, as the movable scroll member 20 orbits, the movable pins 40 slide along outer circumferential surfaces of the associated fixed pins 42.

[0031] When the crankshaft 14 rotates, the movable scroll member 20 which can relatively rotate with respect to the crankshaft 14 orbits about the axis of the drive shaft 8 without rotating.

[0032] As the movable scroll member 20 orbits, the refrigerant gas introduced into the intake space 45 through the inlet 44 is closed in the compression chamber 32 and is moved toward the center of the movable scroll member 20 while compressed and highly pressurized. The most highly pressurized refrigerant gas in the compression chamber 32 flows into the discharge chamber 25 through the discharge port 50 which is defined at the center of the movable scroll base plate 24.

[0033] The compressed refrigerant gas passing through the discharge port 50 and the discharge valve 52 is discharged into the first pressure chamber 70 inside the boss 24 a. The first pressure chamber 70 communicates with the inside of the motor housing 6 through a first passage 82 formed within the drive shaft 8 including the crankshaft 14. The refrigerant gas flowed into the motor housing 6 is discharged from a second passage 84 formed within the drive shaft 8 to an external refrigerant gas circuit through an outlet 86 which is formed through a wall of the motor housing 6. The motor is cooled by the refrigerant gas which flows from the first passage 82 to the second passage 84.

[0034] As shown in FIG. 3, the spool valve 62 is accommodated in the movable scroll base plate 24. The pressure in the second pressure chamber 72 is applied to the first end surface 62 a of the spool valve 62 through the first pressure port 66 while the compressor is driven. The pressure in the compression chamber 32 in a predetermined compression period is applied to the second end surface 62 b of the spool valve 62 through the second pressure port 64. That is, pressure in the sealed space is applied to the second end surface 62 b while the movable scroll member 20 orbits by an angle of 360 degree in a compression process of the refrigerant gas. The pressure has a predetermined range.

[0035] Still referring to FIG. 3, when the pressure in the second pressure chamber 72 is lower than the pressure in the compression chamber 32, the spool valve 62 is pushed against the stopper 68 to close the communication passage 60. When the pressure in the second chamber 72 is higher than the pressure in the compression chamber 32, the first end surface 62 a of the spool valve 62 does not contact the stopper 68 to open the communication passage 60. When the communication passage 60 communicates between the second pressure chamber 72 and the intake space 45, refrigerant gas in the second pressure chamber 72 flows into the intake space 45 through the communication passage 60. That is, every time the movable scroll member 20 orbits by an angle of 360 degrees, the spool valve 62 opens and closes the communication passage 60 due to difference between the pressure in the compression chamber 32 in the predetermined period of the compression process of the gas and the pressure in the second pressure chamber 72, thus controlling the pressure in the second pressure chamber 72.

[0036] In the above embodiment, the following effects are obtained.

[0037] As described above, in the embodiment of the scroll compressor and a method for controlling back pressure for the scroll compressor according to the present invention, the pressure in the second pressure chamber 72 is controlled by the spool valve 62 through the communication passage 60. For the above reason, thrust force by which the movable scroll member 20 is pushed against the fixed scroll member 2 is properly controlled in a predetermined range. Therefore, wear of the fixed scroll spiral wrap 28 and the movable scroll spiral wrap 30 caused by the excessive thrust force of the movable scroll member 20 is suppressed and power loss is reduced. Since the pressure in the second pressure chamber 72 is controlled due to the difference between the pressure in the compression chamber 32 in the predetermined period of the compression process of the gas and the pressure in the second pressure chamber 72, a spring is not required. As a result, a simple mechanism for reliving pressure is offered.

[0038] Furthermore, in the embodiment, the spool valve 62 has a step. Since the area of the first end surface 62 a to which the pressure in the second pressure chamber 72 is applied is larger than that of the second end surface 62 b to which the pressure in the compression chamber 32 is applied, the pressure in the second pressure chamber 72 is controlled to be substantially lower than that in the compression chamber 32. The pressure in the second pressure chamber 72 is properly controlled by varying difference between the area of the first end surface 62 a to which the pressure in the second pressure chamber 72 is applied and that of the second end surface 62 b to which the pressure in the compression chamber 32 is applied. Also, the pressure in the second pressure chamber 72 is controlled by varying a position of the second pressure port 64 for communicating with the compression chamber 32, which is formed in the movable scroll base plate 24.

[0039] In the present invention, the following alternative embodiments are also practiced.

[0040] In the above embodiment, the pressure in the second pressure chamber 72 is relieved to the intake space 45 as an intake system. However, the pressure in the second pressure chamber 72 is also relieved to the compression chamber 32. At this time, it is desired to return to a low pressure region where compression of refrigerant gas in the compression chamber 32 has just begun. In this case, it is more efficient to suppress reduction of efficiency than returning to the intake system.

[0041] The spool valve 62 opens and closes the communication passage 60 due to the difference between the pressure in the compression chamber 32 in the predetermined period of the compression process of the gas and the pressure in the second pressure chamber 72. However, the spool valve 62 does not need to be completely closed, and instead may restrict an orifice to regulate flow. In addition to the difference in pressure, a resilient force by a spring, as an auxiliary force may vary an opening amount of the communication passage 60. That is, the spool valve 62 may vary the opening amount of the communication passage 60 due to the difference in pressure and the resilient force by a spring. In this case, degree of freedom for determining the position of the second pressure port 64 is increased. A poppet valve as an opening and closing valve may be used instead of the spool valve 62.

[0042] The refrigerant gas in the compression chamber 32 is discharged through the discharge port 50 formed through the movable scroll member 20. However, the refrigerant gas may be discharged through the fixed scroll member 2 if back pressure is applied to the back surface of the movable scroll member 20.

[0043] As described in detail, in the present invention, a scroll compressor which controls pressure in a back pressure chamber and a method for controlling the pressure in the back pressure chamber for the scroll compressor are offered without a spring.

[0044] The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims. 

What is claimed is:
 1. A scroll compressor for compressing gas introduced from an inlet, the gas being compressed and discharged through a discharge port, the scroll compressor comprising: a fixed scroll member; a movable scroll member having a movable scroll base plate, wherein the fixed scroll member and the movable scroll member cooperatively form a compression region and an intake space communicating to the inlet; a housing secured to the fixed scroll member, the housing accommodating the movable scroll member to define a back pressure chamber, pressure in the back pressure chamber being applied to the back surface of the movable scroll base plate, the back pressure chamber communicating with a region through a communication passage, the region being lower in pressure than the back pressure chamber, the communication passage relieving the pressure in the back pressure chamber to the region; and a valve for varying an opening amount of the communication passage due to difference between the pressure in the compression region in the predetermined period of a compression process of the gas, and the pressure in the back pressure chamber.
 2. The scroll compressor according to claim 1 wherein the region is the compressor intake system.
 3. The scroll compressor according to claim 1 wherein the region is a compression region of the compressor.
 4. The scroll's compressor according to claim 3 wherein the pressure in the back pressure chamber is relieved to the region where gas compression in the compression region has just begun.
 5. The scroll compressor according to claim 1 wherein the valve is a spool valve.
 6. The scroll compressor according to claim 5 wherein the valve has a first end surface and a second end surface in the axial direction of the valve, the first end surface being smaller in area than the second end surface.
 7. The scroll compressor according to claim 1 wherein the valve is a poppet valve.
 8. The scroll compressor according to claim 1 further comprising an auxiliary spring for varying the opening amount of the communication passage, wherein the valve varies the opening amount of the communication passage due to the pressure difference and resilient force of the auxiliary spring.
 9. The scroll compressor according to claim 1 wherein the discharge port is formed in the movable scroll member, wherein the back pressure chamber is constituted of a first pressure chamber, a second pressure chamber and a third pressure chamber, the first pressure chamber receiving the discharged gas in the vicinity of the discharge port, the third pressure chamber communicating with the intake space in the vicinity of the inlet, the second pressure chamber being defined between the first pressure chamber and the third pressure chamber, and wherein the valve varies the opening amount of the communication passage due to difference between the pressure in the compression region in the predetermined period of the compression process of the gas, and the pressure in the back pressure chamber.
 10. The scroll compressor according to claim 1 wherein the communication passage and the valve are formed in the movable scroll base plate.
 11. The scroll compressor according to claim 10 wherein the movable scroll base plate forms a valve chamber for accommodating the valve.
 12. The scroll compressor according to claim 1 wherein the valve is an opening and closing valve for opening and closing the communication passage.
 13. A method for controlling the pressure in a back pressure chamber of a scroll compressor for compressing gas in a compression region comprising the step of: communicating the back pressure chamber with a region that is lower in pressure than the back pressure chamber in accordance with the difference between the pressure in the compression region in the predetermined period of a compression process of the gas, and the pressure in the back pressure chamber.
 14. The method according to claim 13 wherein the lower-pressure region is the compressor intake system.
 15. The method according to claim 13 wherein the lower-pressure region is a compression region of the compressor.
 16. The method according to claim 13 wherein the communicating step includes passing through a movable scroll base plate.
 17. The method according to claim 13 further comprising the step of accommodating a valve in the movable scroll base plate.
 18. The method according to claim 13 further comprising the step of providing an auxiliary spring in the movable scroll base plate. 